DESCRIPTION The parent project for this FIRCA application is a project within a larger Program Project grant whose PI is Dr. Bruce Weir. Drs. Mackay and Charles Langley are key investigators on Project 6, which is entitled Drosophila Quantitative Genetics. The aims of the parent project are to use QTL mapping methods to characterize the genetic basis of and forces that influence genetic variation of a quantitative trait in Drosophila, bristle number. The parent grant will utilize very creative approaches to clarifying the genetic factors. The goals of the FIRCA grant are to employ a subset of these techniques in order to develop a set of 500 recombinant inbred (RI) strains from natural populations of Drosophila in order to characterize the genetic loci that may influence longevity. Using QTL methodology, the strains will be backcrossed to the parental lines, and a 2cM dense marker map (using insertion sites of roo transposable elements)will be employed. Evidence for QTL to longevity will be scored by the difference in mean trait value between marker classes. The investigators then will extend the QTL analysis to examine gene x environment interaction by changing the environment of the flies from optimal conditions (25oC) to stressful (14oC and 29oC) and measure changes in longevity.